The influence of task characteristics on the intermanual asymmetry of motor overflow

The two studies reported here were designed to test the proposition that greater motor overflow occurs when movements are performed by the non-dominant hand. Unlike previous studies using normal adults, the task in these studies did not require force production. In the first study, a group of 19 right-handed participants performed unweighted finger lifting. That the frequency of motor overflow occurrence was the same regardless of which hand performed the task, did not support findings from other studies where tasks involving force production resulted in more overflow when performed by the non-dominant hand. To investigate further the influence of task characteristics on motor overflow occurrence, in the second study participants were required to remember and reproduce a prescribed sequence of four finger lifts. Left- and right-handed participants (N = 30) performed both single and sequenced finger lifting. The relative frequency of motor overflow (unintended lifts of fingers of the passive hand) was compared between hand preference groups, active hand and task type (single/sequenced). Contrary to the expectation that motor overflow would be greater for the sequenced finger lifting task, overflow was exhibited with a significantly greater frequency on single finger lifting. This finding indicates that task characteristics influence the pattern of overflow occurrence in normal adults. The task used in this study did not involve force production and did not result in an intermanual asymmetry of motor overflow. This contrasts with findings from other studies requiring adults to exert forces where greater overflow occurred when the non-dominant hand was active. However, this study confirms previous findings which show that left-handers produce greater overflow compared to right-handers regardless of the task being performed and the hand performing the task.